(1) Field of the Invention
The present invention concerns a shift control system of an automatic transmission for a vehicle, and more particularly a shift control system of an automatic transmission for a vehicle, which employs a lay shaft to constitute a power train with three shafts and five speeds.
(2) Description of Prior Art
The automatic transmission carries out a gearshift by means of a transmission control unit (TCU), which controls solenoid valves to regulate the hydraulic pressure flow according to the vehicle speed or the degree of the acceleration pedal being pressed down. It also employs the hydraulic pressure to control the clutches for associating rotational members, and friction elements such as brakes for fixing the rotational elements to change the ratio of the gearshift of a planetary gear system. This is achieved by selecting the input elements for receiving the engine power and the reaction element, which selection is accomplished by the shift control system. Generally, the shift control may be complicated or not according to the procedure to control the friction elements.